Among the wood preservatives used in the last two decades for making outdoor wood constructions such as decks, chromated copper arsenate (CCA) has been the most popular. However, as arsenic is a known carcinogen, the U.S. Environmental Protection Agency (EPA) and wood preservative industry have reached agreement, effective Dec. 31, 2003, to employ less toxic alternatives.
Two such alternatives, Alkaline Copper Quat (ACQ) and Copper Azole (CA), have been approved by the American Wood Preserver's Association for outdoor use. However, the present inventors believe these new treatments can create a serious problem in that they are more likely than CCA to accelerate the corrosion of metal fasteners that are typically are used in assembling wood decks. While all of these preservatives contain copper, which can leach out of the wood and deposit as an oxide on the metal fastener, thereby creating a galvanic potential and thus oxidation and corrosion, the inventors realize that CCA contains an anodic inhibitor (chromate) and a cathodic inhibitor (arsenate) to slow down corrosion, whereas ACQ and CA do not.
The present inventors believe that without such inhibitors ACQ and CA will facilitate corrosion in metal fasteners as well as in metal “joist hangers” and other metal connector devices used in deck assemblies and other outdoor wood constructions. Certain forms of ACQ, moreover, contain chlorides that exacerabate the corrosion problem. Failure of joist hangers could lead to injury or death, and must be avoided. Although decay resistant woods (e.g., redwood, cedar), woodfiber/plastic composites, and/or stainless steel fasteners and devices can be substituted, these are all far more expensive than using common stock lumber, fasteners, and joist hangers.
A less expensive method for assembling outdoor wood structures is needed.